1. Field of the Invention
This invention relates generally to planetary transmissions. More specifically, this invention is related to a three-speed planetary transmission.
2. Description of the Prior Art
There are known a great many arrangements of planetary transmissions for providing various speed ratios from a drive shaft to a driven shaft. These transmissions often use multiple planetary and ring gear sets to provide various speeds. U.S. Pat. No. 2,755,688 issued to Swennes illustrates a planetary transmission for providing two forward and one reverse speeds and is only one example of the use of multiple ring gear and planetary systems to provide the speed changes. It is well known that such transmissions provide the advantage of allowing speed changes without disengagement or movement of gears. Another system showing a multiplicity of planetary elements in combination with control means such as brakes and one-way clutches for obtaining desired speed ratios is shown in U.S. Pat. No. 2,308,082 issued to Johnson. However, as Swennes and Johnson demonstrate, such systems usually employ numerous interconnections for coupling planetary carriers, ring gears and sun gears which make the resulting transmission bulky and expensive to fabricate.
Accordingly, it is an object of this invention to provide a planetary transmission having a reduced number of operating elements, a simple method of controlling speed changes and a compact design that is more straightforward in operation.
It is a further object of this invention to provide a planetary transmission in which planetary elements may be nested to reduce the overall size of the transmission.